1. Field of the Invention
The present invention generally relates to dental tools and instruments and pertains particularly to a method and apparatus for removing obstructions, such as portions of instruments that break off and become stuck during endodontic and retreatment procedures, from root canals. More particularly, the invention relates to a set of microendodontic instruments precisely designed and machined to remove a broken instrument from deep within the root canal space.
2. Discussion of the Related Art
The human tooth is subject damage and injury from many sources over its life. A tooth comprises a crown and root, with the crown having a thin outer layer of enamel covering an underlying tubular dentine. The root's outer layer is comprised of a thin layer of cementum which covers the radicular dentine. Located generally central within these hard tissue structures is a soft tissue called the dental pulp which provides the vascular support and neural supply for the tooth.
The dental pulp is the most vulnerable and may be injured, requiring various treatments or repairs. Options for treatment include palliative emergency care, endodontics (i.e., root canal treatment), or extraction. Retreatment or extraction is necessary when prior treatment fails. Root canal treatment and retreatment includes cleaning and shaping of the root canal space with instruments commonly referred to as "files". There are a great variety of file choices ranging from different metals to flute configurations and geometries, tapers, lengths, and handle designs. During cleaning and shaping, the potential for file breakage is always present.
Retrieving broken instruments or other intercanal obstructions, such as gates glidden drills, lentulo spirals, silver points, and obturation carriers, pose formidable challenges because instruments can break at any point in the canal. If the coronal end of the broken instrument is near the crown of the tooth, the instrument can be removed fairly easily using traditional or conventional techniques. However, if the instrument breaks deep within the root canal, for example, where the canal begins to bend or curve, extraction of the instrument becomes much more difficult.
There has not been available any retrieval tools that can reach deep into the root canal, and thus are useless for broken instruments. Also, if the practitioner was still in the process of cleaning and shaping the root canal when the instrument broke, there can be bacteria, pulp, endotoxins, etc. deeper in the root canal that still needs to be removed. Thus, breakage of the instrument deep within the root canal can severely impact the outcome of the endodontic procedure. Typically, such instrument breakage results in tooth extraction or apical surgery to seal off the end of the root to prevent the bacteria, pulp, endotoxins, etc. from leaking out the end of the canal.
Some instrument retrieval techniques have been developed over the years. However, many of these methods were crude, ineffective, and limited by restricted space. Traditionally, small files were used in efforts to either bypass or eliminate broken instruments. In other efforts, varying diameter tubes have been proposed for placing over the most coronal end of the obstruction to be used in a variety of ways to retrieve obstructions. The tubes have been attached to the obstruction by various means such as glue, mechanical friction, or internal threads which engage certain broken instruments. For instance in U.S. Pat. No. 5,879,160 a system is proposed using a hollow tube in which a plunger with a beveled end is slid in order to engage the obstruction. However, the system requires the plunger to be slid into the tube and aligned so that the bevel is oriented towards the obstruction in order to force it into a cutout. This limitation makes the system more difficult to use because it requires radial alignment of the tube and plunger in accordance with each other as well as the obstruction. It is also less effective because failure results when the beveled edge fails to force the obstruction into the cutout. Moreover, it is less successful because there is no mechanism for securing the plunger to the tube when engaging the obstruction.
Frequently, such efforts, even when successful, weakened roots due to overzealous canal enlargement, which in turn predisposed the tooth to subsequent root fractures and, ultimately extraction of the tooth. Additionally, prior techniques lead to perforation of the root or the creation of ledges within the root canal, altering prognosis. Moreover, if retrieval efforts were unsuccessful, cleaning and shaping procedures and obturation are compromised putting the ultimate prognosis in doubt. Furthermore, a small but statistically significant number of broken instruments can not be retrieved even with all of these innovations, technologies, and techniques.
Therefore, a more successful, effective, and easy to use tool and method for removing broken instruments and other intercanal obstructions from root canal systems is needed.